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DIY: Do It Yourself Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

I too needed to replace one fob's battery and found this thread and it was very helpful. I was able to open up the key fob and unsolder the battery and was about to order the horizontal battery from Mouser or Digikey. Before I did, I researched the battery on the Panasonic battery site and found that another non-rechargeable is essentially the same size and voltage. I picked one up at my local drug store (2025 or equivalent). Now, here is the part that you may or may not want to try (see picture). After removing the battery, I used needle nose pliers to roll the welded tabs off like you do to open a can of sardines (those who remember using the included key to remove the metal strip around the can). I then smoothed them back out flat and soldered both battery contacts back on without the battery (you may actually trim off the battery contact wrinkly part if you want). This makes like a slip-in battery holder. I slipped in the battery, wrapped a rubber band around the fob and tried it. It works great! Yes, I know this is not a rechargeable, but I could not find anything on the circuit board that takes an outside electrical source that could possibly recharge the battery (I will do some more research, but I don't think it HAS to be a rechargeable type battery). The only other significant difference between the rechargeable and the 2025 lithium I used is a specification for Nominal Capacity (mAh). The rechargeable is lower at 7 as opposed to the 2025 which is 165 mAh which means it should last longer! Well I have been using mine for a total cost of less than $3 now for over 7 months and it's still going strong. Just in case though, I used a silicone sealer type adhesive that is strong but removable if I have to change the battery. The beauty is that if there is a next time, I just slip out the old battery and slip in a new $3 battery and reseal (no more soldering). The plastic holder the fob has for the battery space puts enough pressure on the slip-in cell so you don't have to use the solder variety. Hope this helps - good luck. Donald (electronics engineer) San Francisco.

Donald, I used your technique yesterday for two keys. I used a 2025 in one and a 2016 in the other. Both worked! The bottom battery lead pops out and does not need to be soldered in. I actually tried soldering this on my second try with no luck (amateur I guess), but the pressure of the key enclosure is enough to keep the lead in place. Thanks to everyone on this board, you just saved me $400!!!!

My wife's key to our '01 330i had stopped working. After reading this thread, I opend the key to find that one of the solder joints had come loose. I just resoldered it and tried it in the car (after a year of not charging!), shazam! it fired right up. Kudos to all, $200+ for a key is robbery.

Ok, I ordered a key off ebay, opened my original key and took the circuit board out and soldered in a new battery. The key worked great for about 4 months, but now it doesn't lock or unlock the doors any more. I also had to have the key cut (which all my local BMW stealerships said couldn't be done) I found a locksmith that could do it. So from this I am assuming that my car isn't charging the battery. Does anyone know if there is a way to verify that the key is charging while in the ignition?

A BIG thank you to the OP. The previous owner had given me two keys and I thought that one of them did not work. I charged the "dead" key by driving to/from work, and reprogrammed the key by utilizing the OP's instructions. It worked! I now have two working keys. Thank you, again, OP.

Not sure if it's been mentioned in the thread because I didn't have the time to read through it all, but I wonder if our keys would recharge using one of those new "charging pads" they sell for cell phones. One of my keys' battery is dead. I may splurge on the pad for $20 and see how this goes. If I do remember to buy it, I'll post the results. I highly doubt it because it's a different type of battery, but you never know.

I worked round the seam of the key first with a junior hacksaw, starting at the key fob end, to remove the majority of the material. The blade fits neatly in the seam and this is quick and relatively easy to do, with less risk of damage to the key or your fingers. I finished off with a hobby knife with the blade set to 2 or 3mm and then prized open with flatblade screwdriver.

It's important to get those soldered joints as thin as possible as it is a tight fit in the battery compartment. I skimmed off a bit of excess solder with a dremmel (make sure the electronics are covered so you don't spray the pcb with metal filings.

Just found this thread. I bought a 03 M and one of the keys is dead. I took it apart tonight with a very thin hobby saw (from hobby saw) and it worked awesome - very clean cutting. Its kind of like the saw above, but with a blade about 1/2 as thick - fit in the grooves perfectly and made straight cuts. I started at the ring hole side and went around till I got to the metal part of the key. I was cutting this a bit, and realized that if I pried it up a bit, I only had to get a 1/4" or so of clearance before being able to pry the board out gently. The good part about not totally separating the two halves is that it will go back together much easier and cleaner later - just throw some epoxy on and zip tie the ring side as one other person did here.

To shed some light based on the other posts in here:

- the squiggly line on the board is actually the antenna. It is squiggly so that the projection pattern of the RF spreads out. Based on the little I know about RF, I would say that the longest distance will be acquired with a very slightly downward tilt, pointing the metal part of the key towards the car.

-For those who are using cr2032 or cr 2015 batteries in place of the stock Panasonic rechargeable, I would not recommend this! Even though it may work, when the key is in the ignition, it is still applying a charge to the battery via the induction coil (thats the 1/2" long copper looking thing on the board). Although this current is definitely small, lithium batterys can explode if not properly charged and peaked. I wouldn't be surprised if a few of those batteries were found leaking after some time. Folks, take the extra couple days and get the correct battery.

-For those with issues after gluing it back together... Careful that the battery is not forcing the tabs/legs from the board. Solder pads on pc boards like that are not designed to take heavy loads and will eventually fail. Also, for those that couldn't get this to work at all, make sure you are keeping the (+) side up.

The tabs are close in proximity to the original ones where hey hit the board, and it looks like just a little bending will be required. I will be desoldering the current battery via the leads and soldering the new tabs on. Its a very easy solder job with my favorite low wattage iron.

The tabs are close in proximity to the original ones where hey hit the board, and it looks like just a little bending will be required. I will be desoldering the current battery via the leads and soldering the new tabs on. Its a very easy solder job with my favorite low wattage iron.

Great thread... thank you for sharing. My key works fine but I found a new "shell" for only $8. My shell is a bit worn and scratched up so I'm going to swap the shell and the metal key part. You pics helped me see that it is all possible. Thanks!